Nouns

(n)lightweighta professional boxer who weighs between 131 and 135 pounds
(n)whippersnapper, jackanapes, lightweightsomeone who is unimportant but cheeky and presumptuous
(n)lightweightan amateur boxer who weighs no more than 132 pounds
(n)lightweighta wrestler who weighs 139-154 pounds
(n)lightweightA weight class division in combat sports, for fighters heavier than those in the featherweight division and lighter than those in the welterweight division.

Adjectives

(s)lightweightweighing relatively little compared with another item or object of similar use“a lightweight fabric”, “lightweight wood”
(s)lightweighthaving no importance or influence“a lightweight intellect”